Qt Stylesheet. Background-color, YES. background-image, NO

Question

It's a weird problem with stylesheets: I have a window, child of class QWidget. I apply a stylesheet to it to ideally change the background of the entire window to an image with a repeat-x and repeat-y, tiling it.

The stylesheet "pipeline" works. If I use "background-color" and set it to say, red, the entire window will be painted red. however, if I use the background-image, it does not. if i add a CHILD WIDGET (using Qt-Designer) inside the window, the background-image will work, just inside that child widget, but not outside of it, all over the parent window.

Obviously I am doing something wrong, but am really clueless as to why the background-color would work on the entire window, but the background-image won't, unless there's a child widget, and then, only inside of it.

Answer 1

I had a similar problem and it was solved by reading Qt Stylesheets docs.

As it is said in the Qt's stylesheets reference, applying CSS styles to custom widgets inherited from QWidget requires reimplementing paintEvent() in that way:

void CustomWidget::paintEvent(QPaintEvent *)
{
    QStyleOption opt;
    opt.init(this);
    QPainter p(this);
    style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
}

Without doing it your custom widgets will support only the background, background-clip and background-origin properties.

You can read about it here: Qt Stylesheets reference in the section "List of Stylable Widgets" -> QWidget.

Hope, it will help!

Answer 2

I know this is kind of an old question, but I stumbled across it because I was having the exact same problem.

It turns out if you create your widget as a subclass of QFrame instead of a QWidget, the background-image property seems to take fine. Also , as Dave's example shows, if you just create a "raw" QWidget, it also seems to work fine. For whatever reason, if you create a new widget derived from QWidget, background-image no longer works.

If you create your widgets in Qt Designer or Creator, they don't have an option to create a QFrame-derived widget, so I just tell it I want a QWidget-derived class, then manually change the .cpp and .h file to derive from QFrame instead of QWidget.